Certain network devices may be classified as heterogeneous in that they may accept data of many different types and forward such data (for egress) in many different formats or over different types of transmission mechanisms. Examples of such devices include translating gateways which unpackage data in one format and repackage it in yet another format. When such devices merely forward data from point to point, there is little need to classify packets that arrive at such devices. However, in devices where there are multiple types of ports which may act as both ingress and egress ports, and further in devices where physical ports may be sectioned into many logical ports, there is a need for packet classification. In some of these devices, where the devices also provision multicasting of data, packets must often be stored in queues or memories so that they can be read in turn by all of the multicast members (e.g. ports) for which they are destined.
FIG. 1 illustrates a heterogeneous network environment which provides different types of services and marries different transport mechanisms. A network ring 100 may include a high capacity network such as a SONET ring and usually provides service to more than one customer. Such customers may distribute the service they receive to one or more nodes behind their own internal network. FIG. 1 shows nodes 110, 120, 130, 140, 150 and 160. Nodes 140 and 150 are accessed via the same Customer Premises Equipment (CPE) network device 180 while the other nodes are shown directly accessing the ring 100. CPE 180 may be a gateway which apportions transport mechanisms such as Ethernet or PDH (such as a T1 or T3 line) over the ring 100 making use of the bandwidth given thereby. As mentioned above, ring 100 is a carrier-class network which may have a very large bandwidth such as 2.5 Gb/s. As such, ring 100 is not like a typical Local Area Network or even a point-to-point leased line.
While network elements could simply be built with many different physical line cards and large memories, such cost may be prohibitive to a customer. Further, where the customer seeks to utilize many different channels or logical ports over the same physical ingress or egress port, such solutions do not scale very well and increase the cost and complexity of the CPE dramatically. Recently, there are efforts underway to provide scalable network elements that can operate on less hardware and thus, with less cost and complexity than their predecessors but still provide better performance. In such efforts, policing access to and the allocating of physical resources of the network elements (e.g., buffer memory and processing cycles) are vital. Buffers can either be shared by different flows/ports or dedicated or some combination of the two. Buffers may also be implemented in internal or external memory depending upon system design and cost constraints. Buffers whether shared or dedicated may become full or be overutilized by a particular service, port or flow.
In such cases, a mechanism is needed to determine when such resources are exhausted and when packets can be dropped by the network element in order to properly allocate available buffer space to other flows, ports and services, as desired. Although some mechanisms have been implemented to manage buffer usage, these mechanisms are constrained by configuration and often cannot adapt to changing traffic profiles.